If they were as cheap as pizza pans, I imagine that many of our members would use them. They are more aerodynamic than flat covers, right? Sturdy, actually attractive, and some people actually know what they are and why to use them.

However:
They are prohibitively expensive.
They do not have a good method of attachment.
Prone to scratching.
I forget what else I was thinking, but I will add to that list as we come up with more limitations.

I was thinking that if you took one moon cap, made a plug of it, and then cast an ABS disc, with a large hole in the middle, and a metal ring on the inside, and then insert pieces that match different lug patterns, and shaped washers that go between the lug nut and wheel, extending out to secure the cover. Then you screw in or otherwise attach a lug nut cover.
What parts of that do not make sense?

They are (prohibitively?) expensive. (how much for the raw alumum sheet?)
They do not have a good method of attachment. (Dzus fasteners)
Prone to scratching. (Jack the wheel up, spin it and sand them out with 200 grit sandpaper)

How about it's hard to move the valve stem to the inside of the wheel and fill the tire from there? Or accommodating wheel weights?

Chuck the sheet ABS in a lathe and use a roller on each side similar to clay on a potter's wheel. Casting won't get the best result.

I'd like a set, but the only source I've found so far is eBay, and they're expensive and don't even ship to Europe. (I'd never make back the fuel savings if I spend $100 for a set, then an unknown amount for shipping)

So I guess pizza pans or flat plate disks it is, since I don't own a lathe.

I'm getting ready to find out their limitations, since mine arrived last night. I just need to re-furb them and I'll be installing them by the weekend.
My clutch switch, throttle smoothing circuit and regen switch also arrived, so they'll be hooked up this weekend also!

I'm getting ready to find out their limitations, since mine arrived last night. I just need to re-furb them and I'll be installing them by the weekend.
My clutch switch, throttle smoothing circuit and regen switch also arrived, so they'll be hooked up this weekend also!

That's the idea, to get it to hold tight to the wheel. I'm afraid the nylon washers would let it loosen over time, but I could be wrong. I need the screws to stay put until I pop them off every other week or so to air up the tires, but not be so permanent that I get lazy and let the psi's suffer.